1. Field of the Invention
This invention relates to a semiconductor controlled rectifier having an amplifying type gate structure.
2. Description of the Prior Art
When a triggering voltage is applied between the gate and the cathode electrode of a semiconductor controlled rectifier, e.g. a thyristor, to cause a gate current to flow, with the forward voltage applied between the anode and the cathode thereof, the forward blocking PN junctions of the semiconductor controlled rectifier break over to cause a current to flow between the anode and the cathode. The change of the thyristor from its cut-off state to its conducting state is called the "turn-on" of the thyristor.
The turn-on of the thyristor begins with the turn-on of that small area of the thyristor which is on the periphery of the cathode and nearest to the gate electrode and the turned-on or conducting area expands up to the whole body of the thyristor. Accordingly, if the rate di/dt of rise of the forward current with time in the early stage of the turn-on operation has a great value, a high forward current will flow through a small conducting area to make the current density very high so that the power loss in that area may become so large as to destroy the thyristor in some extreme cases. In order to overcome such a drawback, a thyristor of amplifying gate type has been proposed which has an auxiliary thyristor region (U.S. Pat. No. 3,526,815). Such a thyristor has an auxiliary thyristor region and a main thyristor region formed integrally and parallel in the same semiconductor substrate, and the auxiliary thyristor region is first turned on by a triggering signal and the turn-on current, i.e. the current flowing through the auxiliary thyristor region, is used as a triggering signal for turning on the main thyristor region. Accordingly, the forward current in the early stage of the turn-on phenomenon divides into the main and auxiliary thyristor regions. Thus, the switching energy is shared to both the regions so that the di/dt capability in the early stage of turn-on can be considerably increased.
However, it has shown that the recently increasing demands for rectifiers having higher breakover voltage, greater current capacity and higher switching speeds necessitate further improvements in such an amplifying gate type thyristor. Namely, it has been revealed that if in this type of thyristor the main thyristor region is simply provided with an auxiliary thyristor region in the vicinity thereof, electric or thermal breakdown easily takes place in the auxiliary thyristor region and in its neighborhood and therefore that the di/dt capability cannot be sufficiently increased.